Generally, a fuel cell is an energy conversion device that generates electrical energy through an electrochemical reaction between a fuel and an oxidizer and has an advantage that electric power can be consistently generated as long as the fuel is continuously supplied.
A polymer electrolyte membrane fuel cell (PEMFC), which uses a polymer membrane capable of permeating hydrogen ions as an electrolyte, has a low operating temperature of about 100° C. or less as compared to other types of fuel cells, and has advantages of high energy conversion efficiency, high output density and fast response characteristics. Besides, since it can be miniaturized, it can be provided as portable, vehicle and household power supplies.
The polymer electrolyte membrane fuel cell stack comprises a membrane-electrode assembly (MEA) having an electrode layer formed by applying an anode and a cathode, respectively, around an electrolyte membrane composed of a polymer material, a gas diffusion layer (GDL) for serving to distribute reaction gases evenly over the entire reaction region and to transfer the electrons generated by the oxidation reaction of the anode electrode toward the cathode electrode, a separating plate (bipolar plate) for supplying reaction gases to the gas diffusion layer and discharging the water generated by the electrochemical reaction outside, and a gasket of rubber materials with elasticity for preventing leakage of the reaction gases and the cooling water by being disposed on the outer circumference of the reaction region in the separating plate or the membrane-electrode assembly.
Conventional separating plates for a fuel cell stack are configured such that the flows of the reaction gas and the resulting water travel in the same direction through two-dimensional channels or are distributed and discharged through intersecting three-dimensional solid shapes. However, they have a structure that is not suitable for efficiently discharging a variable amount of water under various operation conditions, thereby having a problem of deteriorating the performance of the fuel cell stack.